The invention pertains to semiconductor processing methods of removing conductive material.
Conductive materials are frequently formed over semiconductive materials during fabrication of semiconductor chips. In typical processing, a circular wafer of semiconductive material is processed to have one or more thin conductive layers formed thereover. The conductive layers can comprise, for example, metal (such as, for example, copper, aluminum, titanium, tantalum, iron, silver, gold, etc.) or other conductive materials (such as, for example, conductively doped polysilicon). The conductive materials can be subsequently planarized by, for example, electrochemical-mechanical planarization. In electrochemical-mechanical planarization, the conductive material is exposed to an electrical circuit which causes at least some of the conductive material to be electrochemically removed and the material is simultaneously exposed to polishing conditions. The polishing conditions enhance removal of the conductive material and planarize a surface of any remaining conductive material. The polishing can be accomplished by, for example, abrasively removing the conductive material with a polishing pad and polishing slurry.
A difficulty associated with electrochemical-mechanical planarization processes can occur in attempting to maintain a circuit through a conductive material during a simultaneous electrochemical removal and polishing process. It is typical to utilize some portions of the conductive material for carrying current to other portions during the electrochemical removal. For instance, peripheral edges of the conductive material can be connected to a cathode terminal of a power source, a polishing pad connected to an anode terminal of the power source, and the conductive material utilized to complete a circuit between the anode and cathode terminals. A problem which can occur as portions of the conductive material are removed is that such can break an electrical connection to other portions of the conductive material. The breakage of the electrical connection can slow or stop electrochemical removal of such other portions of the conductive material.
In particularly problematic instances, some portions of conductive material will be entirely removed from around other portions of conductive material to leave such other portions as islands surrounded by electrically insulative materials. Such islands will thus have no electrical connection between the anode and cathode, and will not be subjected to electrochemical removal conditions. Accordingly, the removal of the islands will occur entirely through mechanical polishing and will be slowed relative to removal of conductive materials exposed to both electrochemical removal and mechanical polishing. Accordingly, there will be non-homogeneous removal of conductive materials from over a surface of a wafer.
It would be desirable to develop methods of electrochemical removal that avoided some or all of the above-discussed problems.
In one aspect, the invention encompasses a semiconductive processing method of electrochemical-mechanical removing at least some of a conductive material from over a surface of a semiconductor substrate. A cathode is provided at a first location of the wafer, and an anode is provided at a second location of the wafer. The conductive material is polished with a polishing pad polishing surface. The polishing occurs at a region of the conductive material and not at another region. The region where the polishing occurs is defined as a polishing operation location. The polishing operation location is displaced across the surface of the substrate from said second location of the substrate toward said first location of the substrate. The polishing operation location is not displaced from said first location toward said second location when the polishing operation location is between the first and second locations.
In another aspect, the invention encompasses a semiconductor processing method of removing at least some of a conductive material from over a surface of a semiconductive material wafer. A polishing pad is displaced across an upper surface of the wafer from a central region of the wafer toward a periphery of the wafer, and is not displaced from the periphery to the central region.
In yet another aspect, the invention encompasses a method of electrochemically removing at least some of a conductive material from over a surface of a circular semiconductive material wafer which comprises radially displacing a polishing pad across the surface of the wafer. The radial displacing occurs only outwardly from a central region of the wafer and not inwardly toward the central region.